AstinaGT Forums - HOW TO: Custom Fibreglass Subwoofer Box for a Mazda 323 Astina

How To:

How To:
- This is just a simple guide to building a custom fibreglass subwoofer box for inside a Mazda 323 Astina hatch, but can realistically be used for any car. I personally researched how make a fibreglass box from many sites, but the best ones were:
- http://chris.pfharlock.com/glass/index.htm - This site explains in detail how to create a fibreglass box specifically for the Astina. The problem I found with this was the final finish he got on the box.
- http://www.rexnet.com.au/forum/lofiv...hp/t71937.html - Not specifically for the Astina, but still explains the process really good.
Remember to do your research before jumping into it.

Materials needed:
- Fibreglass mesh/netting
- Fibreglass resin (around 4L or less)
- Fibreglass resin hardener
- Wood glue
- Brushes (el-cheapo ones will do)
- Mixing sticks (I used metal rulers)
- MDF wood – (3/4” inch for the base and the rest can be ½” inch or less)
- Masking tape
- Aluminium foil
- Containers for mixing fibreglass
- Fabric for stretching over (cotton and fleece ones work good, anything that can stretch greatly)
- Velcro strips
- Resin for carpet
- Terminal cup for the back of the box
It would roughly cost around $120 for materials

Tools needed:
- Electric jigsaw
- Drill with 1/8 bit
- Measuring tape
- Electric sander (this one is not to important)
- Rubber gloves and breathing mask
- Scissors
- Staple gun
- Nail gun

1 – Building the wooden outer shell of the box
For the outer shell of the box, many people use just a wood base, or even completely fibreglass the whole thing. This is just personal preference, but I choose to use wood for majority of the outer shell of the box. This is mainly because it provides more strength, is easy to cut, and when using wood for the top of the box, you won’t have the hassle of fibreglass dripping down and not sticking properly.
Firstly create a base for the box using the wood. Remember, this piece of wood will have some influence on the final shape of the box. I found that the best way to do this was to use the carpet of the Astina boot as a template. Using your jigsaw or cutting tool, cut the base and test fit it, it should fit in pretty close to the plastic moulds in the boot.

http://www.fileden.com/files/2007/2/14/773006/base.jpg

Next, cut small pieces of wood for the whole back of the box. A good way to do this is to cut a template of the shape needed out of cardboard. As you are going along use a nail gun and wood glue to stick the pieces of wood together. Each time, test fit it and make sure it follows the back of the plastic mould. I ended up using some braces just to hold it in the right position; these braces are just temporary and can be taken off later when the fibreglass holds it in place.

http://www.fileden.com/files/2007/2/...nishedwood.jpg

Step 2 – Fibre glassing the outer shell of the box
First of all you must protect your car like there was no tomorrow :eek: . Use a thin and clear plastic sheeting to cover the paint on the bumper, the seats and the carpet. For the section that needs to be fibre glassed use masking tape, make sure there are no gaps.

Next, use aluminium foil and wrap it around the plastic mould and floor, sticking it on with masking tape.

http://www.fileden.com/files/2007/2/...oilmasking.jpg

Use several layers of foil until you are confident that it will not leak through. Put your wood structure right up against the foil – this will push it back a little into the right shape.

http://www.fileden.com/files/2007/2/...ilfinished.jpg
http://www.fileden.com/files/2007/2/...ticprotect.jpg

Ok, once that is done its time to fibreglass. Firstly put your wood structure on top of the foil and if needed use a heavy weight to pin it right up against the plastic mould of the car. Pour your fibreglass resin into a container along with a tiny bit of hardener (only a couple of mL’s, not too sure of the exact amount). Remember not to mix too much as this stuff goes off fast and will very quickly become unusable. Get the fibreglass netting and place it on the foil. With a brush with resin, dab at it until the netting stays on by itself and then brush fibreglass resin all over it. Keep doing this until you covered the whole area with a mixture of the netting and resin. You should make sure that you actually fibreglass more area that is needed, that way you can cut a neat line later. It is very important that you make a strong connection between the fibreglass and the wood. Once finished, wait for it to dry, this may take an hour or longer and then add another layer by doing the exact same thing. After this, it is best to let it dry for many hours or preferably over night.

http://www.fileden.com/files/2007/2/...firstlayer.jpg

Step 3 – Removing and Trimming
In this bit, just simply pull out the fibreglass mould and be gentle with it so the fibreglass does not snap. You can expect the mould to come out with many layers of foil attached to it – try to remove as much of it as possible. Now put it back into your car and you will be happy to see it fits in nicely and tight. Now use a marker and draw the line you want it to come up to –this will determine the final back shape of your box so be careful – and also remember not to go for too much of a tight fit as you still need to carpet it. Use an electric hacksaw, grinder, or any other cutting tool to cut your line. After this test fit it, and re-trim if needed.

http://www.fileden.com/files/2007/2/...6/cutfront.jpg
http://www.fileden.com/files/2007/2/...06/cutback.jpg

Step 4 – Strengthening the box
Put another layer of fibreglass on the box, concentrating on increasing the strength. Make sure you get all the patchy areas and also the joints – such as the joints between the wood and the fibreglass, and even in between the joints of wood – mainly to make it stronger and air tight.

Step 5 – Making the Sub Ring
Your sub should have came with a template, if so, now is the time to use it. You should firstly draw the inner line of the circle onto wood. Now cut it, I just used an electric jigsaw and it seemed accurate enough. For the outer bit try and go more rather than less – this way it’s less likely of snapping.

http://www.fileden.com/files/2007/2/.../ringalone.jpg

Now put your sub into it and make sure it fits. After this cut pieces of wood to mount the ring onto the box. This step is important as the angle of the ring will determine your final shape of the sub, you can use a jigsaw to cut the basic shape of the pieces and then sand them to get the right angle. When mounting the ring make sure your nail/screw into the wood bit of the box and not the fibreglass. Now test fit it again, if you like the angle move onto the next step.

http://www.fileden.com/files/2007/2/...ingmounted.jpg

Step 6 – Fibre glassing the front
Get a material which can stretch a lot, I used an old cotton sheet, although its said that fleece is more suitable as it soaks resin well and dries with less crinkles (thanks to 70NYD for that one). Stretch it very tight over the box and use a staple gun to pin it on the back of the box.

http://www.fileden.com/files/2007/2/...6/material.jpg

Put a layer of just plane fibreglass resin for the first layer, use no mesh. Fibreglass everywhere on the front except for the middle of the ring, even go past the edges a little bit. The resin will go through the material and soak it, after an hour or longer it should be dry. The material may have slight ripples when dry, but don’t worry; the carpet should hide most of this.

http://www.fileden.com/files/2007/2/...rialresin1.jpg

Cut the material which is covering the hole for the sub ring. Now using both mesh and resin fibreglass the inside of the box. Don’t worry about the general area of the box; just mainly concentrate on the corners, especially the joint between the material and the rest of the box. Cut the excess material that you no longer need so that there is a straight and neat line.

http://www.fileden.com/files/2007/2/...immaterial.jpg

Now fibre glass the outside of the box, getting everywhere on the front of the material. Once dried and if needed, apply another layer of fibreglass on the outside to make it stronger. Now test that it fits, and for the first time it should actually look like a sub box. There may be large gaps, but most of those gaps will go by carpeting so don't worry too much.

http://www.fileden.com/files/2007/2/...alsubincar.jpg

Step 7 – Finishing and carpeting
Pre drill holes for your sub to screw in to and make sure your sub sits tight.
I sprayed the outside of my box with a coat of GMH black, just for looks if I ever needed to take the box out. It also helps if the carpet is slightly see-through so you won’t see the material under.
The carpet you use must be very flexible – if it doesn’t flex enough it won’t properly fit the outside of the mould. Now get your resin for the carpet (I don’t remember what it was called but you can easily get it from Bunnings) and brush it onto the outside of the box. Then wrap the carpet around the mould – but make sure there are no air bubbles. Once this is done and the resin is dried, cut the excess carpet – keep some past the edges for more tightness when the box sits inside the car.

http://www.fileden.com/files/2007/2/...rpetfinish.jpg

Test fit it and make sure it fits, hopefully it does and goes right on the edge you want it to. Ok, now a good idea is to put a strip of Velcro between the box and the car – you don’t want your sub to roll out as your driving!

http://www.fileden.com/files/2007/2/...006/velcro.jpg

And now you're done, enjoy your sub!!!Here are some final pics of mine:

http://www.fileden.com/files/2007/2/...6/finished.jpg
http://www.fileden.com/files/2007/2/.../finished2.jpg

ADDITIONAL INFO
Fibreglass safety – Remember to always wear a breathing mask, gloves, and long clothing – fibreglass sticks everywhere and the netting is so itchy you will be feeling it for the next week or so.

Let your sub box out of your car when you’re not working on it – the smell it leaves in your car is very...interesting.

When fibre glassing, cut the fibre glass netting into strips – don’t just put it on in one big go or else it will be very weak.

You can put on the terminal cup at basically any stage – simply pre drill a hole and screw the cup in when the box is finished – but put it on the wood part of the box and not the fibreglass bit.

Before starting, find out the max and min volumes for your sub, the manufacturer of the sub should have this on their site. Then calculate the volume that you estimate your box to be and make sure it is suitable. My box is around 40L or a little bit more.

Can you move the box? It can be easily moved out of the car in under two minutes to get access to the jack and spare tyre. All you need to do is pull it out and disconnect the wiring from the terminal cup.

How is the rattle's?When you put a sub in your car, expect it to rattle! Although in saying this, i was actually quite surprised, the only thing that rattled was my back spoiler.

How does it sound? It sounds awesome! It is hard to compare this to the sound my sub would produce if it was in a normal wooden box, but from what i can hear everything sound wise is perfectly normal.